It probably depends on the theater of operation and tech level, but in most of the published adventures I've seen, where there are marines there is battledress. In MTU, it's standard for marines to be trained in and use battledress unless they are assigned to a technical or other role. Infantry wears the armor.

"Spacers lead a sedentary life. They live at home, and their home is always with them—their starship, and so is their country—the depths of space."

There are divergent canon thoughts on this - it wouldn't be Traveller otherwise would it.

For example in A1 Kinunir the sample ISM Platoon does not have BattleDress for all of the marines, only one of the three ten man squads are so equipped and have the battledress skill.. One of the other squads has marines who all have vac suit skill but lack battledress skill. Most of the third squad lack even vac suit skill.

In the GATU or Lorenverse LKW repeated his statement from JTAS that all ISM are battledress trained, something that has been debated for nearly four decades now.

You would have to fudge LBB1 and LBB4 character generation to grant all ISM battledress skill - there is no such skill in LBB1 although vac suit could at a pinch default to it, and it is possible to generate a character in LBB4 that never receives battledress or vac suit skill, there are many sample marine characters in S:13 Veterans that lack the skill.

From a pure cost factor, I would guess that not EVERY embarked marine group is provided with, or trained on, battledress.

A group of marines on a frigate whose primary task is patrolling the spacelanes 100 light years from the Imperial border would not need battledress. A destroyer on the Zhodani lines would most likely have battledress equipped marines.

Being a US Marine myself, I think of battle dress the same way I think of heavy weapons, so in my mind every Marine would probably be trained to use battle dress but your basic Marine infantryman would not have it issued to him. It would most likely be available from a Marine weapons company or platoon.

Typically, a USMC Marine infantry battalion consists of three rifle companies, a weapons company, and a headquarters and service company. The rifle company consists of a headquarters, three rifle platoons of three squads each, and a weapons platoon with medium machine gun, 60mm mortar, and assault weapon (breaching, demolition, and rocket fire) sections. The weapons company consists of a headquarters, a heavy machine gun platoon, a 81mm mortar platoon, and an anti-armor platoon. I believe the British Royal Marines are pretty close to this make up as well.

Depending on the weapon used with the battle dress, it could also take the place of Marine armor and or artillery.

Character generation does not support every ISM being battledress trained - the 3I is not yanks in space and the more that trope creeps in the worse it gets.
In CT you could argue that every ISM has vacc suit 0 which defaults to battledress 0.

Character generation does not support every ISM being battledress trained - the 3I is not yanks in space and the more that trope creeps in the worse it gets.
In CT you could argue that every ISM has vacc suit 0 which defaults to battledress 0.

The only requirement for battle dress is vacc suit 1+ (TL14+ with vacc suit 2+ for earlier TL) and much like heavy weapons, wouldn't be assigned enmasse.

"Character generation does not support every ISM being battledress trained - the 3I is not yanks in space and the more that trope creeps in the worse it gets.
In CT you could argue that every ISM has vacc suit 0 which defaults to battledress 0."

I didn't mean to imply that Imperial Marines are US Marines. I was just using USMC as a real-world example for how battle dress could be organizationally meted out because I'm familiar with how the USMC operates. But having said that, I don't see why anyone should get their panties in a bunch over someone wanting to model their Imperial Marines after USMC? My Imperial Marines are modeled on British Royal Marines Commandos with their special operations units modeled on a combination of Special Boat Service and USMC Force Recon.

As a former military person myself, I can tell you I was trained on things like a .50cal, M60, 40mm grenade launcher, and a LAW. For a few of those items my training consisted of firing them ONCE (a few I got to play with more than that). But my job in the military was firing 203mm rockets at people and places I never saw.

There is a HUGE difference in being trained on battledress once in basic versus being assigned to a unit of battledress-equipped marines. Like everything else, unless you keep your skills up, you get rusty. And battledress costs far too much to be casual with it. Not to mention if you don't know how to operate it like it's a second skin you potentially become a risk to yourself and your unit. And you aren't very helpful on the battlefield.

So the line would be could you walk around in it? Sure if you comfortable in a vac suit. Could you be an effective military presence? No, not unless you were fully trained in it and kept up your practice. The caveat would be that if you had spent years in it then it's likely your skills, even atrophied, could come back pretty fast.

I’m not so sure. Given the cost differences between battle dress and combat dress (both to purchase and to maintain) it seems likely that battle dress availability would be limited in some way. Ground assault marines wouldn’t leave home without it. Star Marines would likely have it for boarding actions but might not issue it to everyone. Marines who serve as vehicle crew? Unlikely.

Seems more than a worthwhile investment in force multipliers for expensively trained troops.

All of the above is true - except the investment portion. Ground troops are relatively cheap to train, even marines. Pilots are more expensive.

However the other thing not be considered is cost. Battledress is expensive to purchase and not cheap to maintain. The Imperial armed forces would be far stronger if all the non TL-15 equipment was discarded and replaced. That's not possible using their budget.

And not having the most up-to-date equipment is something that every soldier in every nation in every time period has faced. It sounds really great! But it never works out that way.

Marines are going to be few in number, unless the planet has done something very very naughty.

Marines are the infantry of the Navy and are often the first in. The Army is the one that fights and holds worlds, Marines are more smash and get out. Two different jobs, so the two groups are trained and equipped differently.

What do you mean by "Numbers would be either the Imperium Army or hired mercenaries"? Are you saying that the Imperium would deploy mercs instead of it's own forces?